Will an empty for loop used as a sleep be optimized away? [duplicate]

Question

I am looking over some code to review and have come across a busy wait as such:

int loop = us*32;
int x;
for(x = 0;x<loop;x++)
{
    /*do nothing*/      
}

I seem to recall reading that these empty loops can be optimized away. Is this what would happen here or can this work?

Answer 1

The answer is yes, the compiler can optimize out the loop.

Use the volatile qualifier to avoid the optimization:

int loop = us * 32;
volatile int x;
for (x = 0; x < loop; x++)
{
    /*do nothing*/      
}

If you are programming in the embedded world read the documentation of your compiler as they usually provide delay functions that wait for a certain number of cycles or microseconds passed in parameter.

For example, avr-gcc has the following function in util/delay.h:

void _delay_us(double __us);